Figure 1. Oemona hirta (F.) Top row female and bottom row male.

Scale bar =1 cm. Image © The Natural History Museum, London

Lemon tree borer

Oemona hirta

BackgroundThe lemon tree borer, Oemona hirta (Fabricius) (Coleoptera: Cerambycidae) is a

longhorn beetle native to New Zealand, where it is considered to be one of their

most common insects. A single live larva was intercepted in a Wisteria plant

imported from New Zealand to a nursery in West Sussex in October 1983. In June

2010 a number of Wisteria rootstocks imported at the beginning of June from New

Zealand to a nursery in Worcestershire were found to be infested with the larvae of

this insect and were destroyed. In July a live larva was found in another Wisteriaplant in Cheshire that was connected to the previous find by the supplier. Several

other related consignments of Wisteria rootstocks were also imported to other UK

nurseries from the same supplier and have been checked for evidence of

infestation.

Geographical Distribution Native to New Zealand and found throughout both islands. Also reported to be

present in Malaysia.

Host PlantsHighly polyphagous, recorded from more than 40 different plant genera. In its

natural range the hosts include both native plant species and many of the

introduced European species. Recorded host genera include: Acacia, Albizia,Aleurites, Alnus, Aristotelia, Asparagus, Betula, Brachyglottis, Callistemon,Casimiroa, Cassinia, Chaenomeles, Choisya, Chrysanthemoides, Citrus,Clerodendrum, Corylus, Crataegus, Cyphormandra, Cytisusm, Dahlia, Eucalyptus,Euonymus, Hibiscus, Hoheria, Juglans, Koelreuteria, Leptospermum, Macadamia,Malus, Oleana, Persea, Phyllostachys, Pinus, Platanus x, Populus, Prunus, Pyrus,Quercus, Rhus, Ribes, Rosa, Salix, Syringa, Syzygium, Tamarix, Telopea, Ulex,Ulmus, Vitex, Vitis, Wisteria and many more.

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DescriptionAdult: A rather unremarkable brown beetle. Females range in size from 14 - 31 mm in body length,

are larger than the males and have proportionately shorter antennae (Figure 1). Adults of both sexes

are about 3.8 times longer than broad; the elytra or wing cases are clothed in pale yellow hairs

(Figures 2 and 4), but the most distinctive feature is a series of transverse, parallel, raised ridges on

the dorsal surface of the thorax (arrowed) (Figures 3 and 5), a feature most prominent in male

specimens and not present on any of the longhorn species native to the British Isles.

Figure 2. Female Oemona hirta Figure 3. Ridges on the thorax

Figure 4. Male Oemona hirta Figure 5. Ridges on the thorax

Figure 6. Oemona hirta larva

in situ within a Wisteria stem

Figure 7. Oemona hirta larva,

head end showing the dark

brown/black jaws

Larvae: Creamy white (Figure 6) with dark brown to black mandibles (jaws) (Figure 7) and reaching

35 mm in length by 8 mm in width when fully grown. Although they appear to be legless the larvae do

have three pairs of short but inconspicuous legs.

Biology and DispersalIn New Zealand the life-cycle takes at least 2 years to complete. Adults are active from the beginning

of October through to the first week of January, and during this period they mate and lay eggs. Eggs

are laid singly in leaf/stem junctions, bark crevices or in fresh pruning scars with each female capable

of producing about 50 eggs during her life span. On hatching the larvae bore directly into the host and

as they develop form long galleries, with periodic side branches to the surface through which they

eject their sawdust-like droppings (frass). Larvae are present and active throughout the year but when

fully mature (between mid-June and mid-October) they form a cell within the host and pupate. Newly

formed adults remain within the pupal cell until their integument has hardened, after which they

emerge, but they do not become sexually mature until 4 days later. The adults live for about 2 months

and are good flyers. They are most active in the morning between 5 and 7 am and in the evening

between 7 and 9 pm during which time mating occurs.

Detection and Damage The lines of frass ejection holes are one indication of the presence of live larvae, but the feeding

activities of the larvae can also cause small twigs to wilt or die resulting in clusters of dead leaves.

Major damage by larger larvae can weaken branches to the point that they break under wind pressure

of fruit load or may even be girdled and die. In New Zealand, Oemona hirta is of great economic

importance since all commercial citrus varieties are attacked. Although best known as a serious pest

of citrus trees, O. hirta also causes damage to other top fruit and some soft fruit (e.g. blueberry) crops.

Ornamental trees and shrubs are also attacked and forestry crops (Populus) can be damaged. In the

UK top fruit and our native trees could potentially be at risk.

ControlLonghorn beetles are difficult to control because the larvae and pupae develop inside the host and are

protected from foliar insecticide treatments and most predators by the surrounding plant tissue. The

only fully effective way of controlling larvae is to destroy the infested plant. Insecticide sprays may be

effective against adults, provided that adults are contacted by the treatment or consume treated

foliage.

Advisory InformationSuspected findings of Oemona hirta or any other non-native plant pest should be reported to the local

Fera Plant Health and Seeds Inspector or to PHSI Headquarters, Sand Hutton, York.

Tel.: 01904 465625, Fax: 01904 465628

Email: planthealth.info@fera.gsi.gov.uk

Web: www.defra.gov.uk/fera/plants/plantHealth

AuthorsJ. Ostojá-Starzewski, A. MacLeod and D. Eyre

The Food and Environment Research Agency (Fera). September 2010

© Crown copyright 2010

Sand Hutton, York

YO41 1LZ, UK

Tel +44 (0)1904 462 000

Fax +44 (0)1904 462 111

E-mail info@fera.gsi.gov.uk

www.defra.gov.uk/fera